The present invention relates to a rocker arm tilted by a cam to open and close a valve provided to a cylinder head and a method of producing a body of the rocker arm.
As a prior-art rocker arm of this type, there is a rocker arm called an end pivot type that is tilted by a cam on one end side as a fulcrum to open and close a valve on the other end side.
The rocker arm includes a body and a roller mounted to the body for coming into contact with the cam to tilt the body.
The body is formed by bending one metal plate into a substantially U shape in section to have side walls in a pair and facing each other in a longitudinal direction and connecting walls for connecting the opposite side walls on longitudinal opposite ends.
A valve fitting portion into which an upper end of the valve is fitted is provided to one connecting wall and a pivot receiver into which an upper end of a pivot portion disposed in a cylinder head is fitted is provided to the other connecting wall.
A roller is rotatibly supported through a spindle between the side walls in the pair and facing each other in a state in which a portion of the roller projects from a through hole provided between the two connecting walls of the body.
The valve fitting portion is obtained by applying guided-bending processing to the body into a substantially U shape in section and then by applying guided-bending processing to cone connecting wall of the body into a substantially inverted M shape in an end face by pushing the one connecting wall up to midway positions in a vertical direction of the side walls in the pair.
This structure is shown in FIGS. 18 to 20. In these drawings, a reference numeral 50 designates the valve fitting portion, 51 and 52 the sidewalls in the pair, and 53 a connecting wall.
Because the above guided-bending processing is forcible guided-bending processing, defects such as cracking that reduces strength and sinking that reduces accuracy of a shape are likely to be generated in outer surfaces of bent portions between the side walls 51 and 52 in the pair and the connecting wall 53. Such defects are main causes of variations in a width W of the valve fitting portion 50 and a rate of generation of defective items increases.
Therefore, the present inventors have accomplished the present invention with the above circumstances in view. In the present invention, a wall thickness of the connecting wall 53 is increased by gathering wall portions of other areas such as the side walls 51 and 52 to the connecting wall 53 and a lower face of the thickened connecting wall 53 is recessed to form the valve fitting portion 50 recessed upward.
In the present invention, when the wall portions of the side walls 51 and 52 are caused to flow into the connecting wall 53, the wall thickness of the side walls 51 and 52 reduce and rigidity of the side walls 51 and 52 may reduce. In order to avoid reduction of rigidity of the side walls 51 and 52, it is necessary to take measures such as using a thick metal plate for the metal plate as a matrix of the body or changing design of a finished shape of the rocker arm body. Because weight increases in the former while cost of design change increases in the latter, there is room for improvement.
Furthermore, the valve fitting portion of the body may be desired to be disposed in a higher position than the pivot receiver depending on an object for which the rocker arm is used. In such a case, it is necessary to push the valve fitting portion further upward in the prior-art structure and the above defects are more likely to be generated. There is also room for improvement.
Therefore, it is an object of the present invention to provide a rocker arm having such a shape as to avoid generation of the above defects in a producing process and a method of producing a body of the rocker arm.
It is another object of the present invention to provide a rocker arm having such a shape as to avoid increase in weight and change in design in addition to the above shape for avoiding generation of the defects in the producing process and a method of producing a body of the rocker arm.
It is yet another object of the present invention to provide a rocker arm having such a shape as to easily adjust a height position of the valve fitting portion in addition to the above shape for avoiding generation of the defects in the producing process and a method of producing a body of the rocker arm.
(1) According to the present invention, there is provided a rocker arm tilted by a cam to open and close a valve provided to a cylinder head, wherein the rocker arm comprises a body obtained by bending one metal plate into a substantially U shape in section to form side walls in a pair and facing each other and a connecting wall for connecting the opposite side walls and a roller mounted for rotation and for coming into contact with the cam between the opposite side walls of the body, a wall thickness of the connecting wall of the body is increased by flowing of a wall portion of a peripheral portion of the connecting wall, and recessing processing is applied to a lower face of the thickened connecting wall to form a valve fitting portion.
Because the valve fitting portion of the rocker arm of the present invention is formed by applying recessing processing to the lower face of the thickened connecting wall, there are not bent portions between the side walls and the connecting wall for forming the valve fitting portion unlike the prior art. Therefore, defects such as cracking that reduces strength and sinking that reduces accuracy of a shape like in prior art do not occur. As a result, it is possible to suppress variations in a width of the valve fitting portion and to reduce a rate of generation of defective items.
(2) According to the present invention, there is provided a rocker arm tilted by a cam to open and close a valve provided to a cylinder head, wherein the rocker arm comprises a body obtained by bending one metal plate into a substantially U shape in section to form side walls in a pair and facing each other and a connecting wall for connecting the opposite side walls and a roller mounted for rotation and for coming into contact with the cam between the opposite side walls of the body, a wall thickness of the connecting wall of the body is increased by flowing of a wall portion of a peripheral portion of the connecting wall by pressurizing and compressing the peripheral portion and recessing processing is applied to a lower face of the thickened connecting wall to form a valve fitting portion, the metal plate has areas to be formed with the side walls and an area to be formed with the connecting wall and has a overhanging chip at a periphery of the area to be formed with the connecting wall, and the overhanging chip is used as the peripheral portion.
In the present invention, similarly to the rocker arm in above (1), defects such as cracking that reduces strength and sinking that reduces accuracy of a shape like in prior art do not occur. As a result, it is possible to suppress variations in a width of the valve fitting portion and to reduce a rate of generation of defective items.
In the present invention, in addition to the above effects, it is unnecessary to increase the wall thickness of the whole metal plate unlike in the above by using the wall portions of the overhanging chips for thickening the connecting wall, thereby avoiding increase in weight of the rocker arm. Furthermore, because it is unnecessary to change design of the finished shape of the rocker arm body, increase in cost for design change can be avoided.
(3) According to the present invention, there is provided a rocker arm tilted by a cam to open and close a valve provided to a cylinder head, wherein the rocker arm comprises a body obtained by bending one metal plate into a substantially U shape to form side walls in a pair and facing each other and a connecting wall for connecting the opposite side walls and a roller mounted for rotation and for coming into contact with the cam between the opposite side walls of the body, an upper face of a longitudinal one end side area of the connecting wall is disposed in a higher position than an upper face of longitudinal the other end side area in a stepped manner, a wall thickness on a longitudinal one end side of the connecting wall is increased only toward a lower face side by gathering a wall portion from a peripheral portion of the connecting wall, and a valve fitting portion is formed to be recessed upward in the lower face of the connecting wall.
In the present invention, similarly to the rocker arm in above (1), defects such as cracking that reduces strength and sinking that reduces accuracy of a shape like in prior art do not occur. As a result, it is possible to suppress variations in a width of the valve fitting portion and to reduce a rate of generation of defective items.
In the present invention, in addition to the above effects, it is possible to obtain the body in which the valve fitting portion is disposed in the higher position than the pivot receiver by relatively easy processing in which the connecting wall is bent into a stepped shape in the producing process of the body when a height difference is required between the longitudinal opposite ends of the connecting wall of the body so as to conform to a relationship between an upper end position of the valve and an upper end position of a tilting fulcrum in an object for which the rocker arm is used.